There has been a known motion guidance apparatus that includes a track rail and a movable block assembled to the track rail via a plurality of rolling members so that the movable block can make reciprocating motion relative to the track rail along the longitudinal direction thereof.
FIGS. 7 and 8 show typical, known configurations of track rails used in motion guidance apparatus of this type. For example, in a track rail 101 shown in FIG. 7, rolling member rolling grooves 103 to which balls 102 apply loads are formed and aligned in the vertical direction, and the head of the track rail 101, when taken along a cross-sectional plane perpendicular to the longitudinal direction thereof, has a diamond shape with right and left corners 104 protruding sideways. When the conventional track rail 101 shown in FIG. 7 are thus configured, the contact angle between the balls 102 and the rolling member rolling grooves 103 can be set along an oblique direction, specifically, the direction inclined by 45 degrees, whereby the ball rows are arranged in such a way that the movable block 105 receives the same load in four directions (radial direction, counter radial direction, and transverse directions). The conventional motion guidance apparatus 100 shown in FIG. 7 can thus be used in any orientation.
Making the loads in the four directions the same as described above is not necessarily achieved by providing the track rail 101 shown in FIG. 7 with the corners 104. Alternatively, it has been known that the loads in the four directions can be made the same by using a track rail 111 shown in FIG. 8, which has a rectangular cross-sectional shape taken along a plane perpendicular to the longitudinal direction thereof. In the track rail 111 having the shape shown in FIG. 8, the contact angle between balls 112 and rolling member rolling grooves 113 can be set along an oblique direction, for example, by skillfully shaping the rolling member rolling grooves 113 or skillfully arranging the rolling member rolling grooves 113 formed on the track rail 111 and rolling grooves 116 formed on a movable block 115 and facing the rolling member rolling grooves 113.